High-end server computing systems are required to maintain very high Reliability, Availability and Serviceability (RAS), typically over 99.99%. One feature of servers that is provided to enhance RAS is referred to as memory hot plug. Memory hot plug allows an administrator to swap out a system memory board, whether to add memory capacity, add memory speed, or do a mirror replace, all in runtime without bringing the system down. The operation includes a hot removal and a hot add.
Since the system processors use system memory to store current states, transactions, instructions and intermediate results, removing a memory board will cause the system to fail. To do a memory hot swap, the system must be configured to allow for such a process.
Typically, such servers provide for handling hot-plug events, using signals to the system that allow the system to accommodate the loss of a memory board before the memory board is removed and to allow the system to allow for the addition of a memory board after one is added. The signals can include an Attention button press, power control, Attention and Power Indicators, Manual Retention Latch sensors etc. These signals are communicated to the platform firmware or BIOS (Basic Input/Output System) and the platform firmware drives the status indicators and power to the memory riser slot that carries the corresponding memory board.
The signals that allow for memory hot swaps are generated, handled, and implemented differently on different hardware platforms and by different designers and manufacturers. They are adapted to different systems by the same designers based on various factors such as routing and placement considerations and form factor. This, in turn, requires parts suppliers to create different parts for different designs or more expensive parts that can be adapted to different designs. It also makes it difficult for administrators to manage systems that use components with different designs. The overall development costs for each system are also higher.